MADISON, Wis. (AP) - With Wisconsin positioned to become the third Midwestern state in as many years to enact a right-to-work law, proponents are touting job growth in Indiana as reason for optimism while detractors say union membership slides in Michigan signal potential problems.

The state’s Assembly began debate Thursday on a plan Republican Gov. Scott Walker has promised to quickly sign and Democrats lack the votes to stop. Following in the footsteps of Indiana and Michigan, the two most recent states to approve legislation making the paying of union dues voluntary, Wisconsin would become the 25th right-to-work state.

The Assembly scheduled 24 hours of debate, planning to wrap up no later than 9 a.m. Friday, and Walker, a likely presidential candidate, expects to sign it Monday.

During the two weeks that the bill rocketed through the Legislature, both supporters and opponents turned to the experiences of Indiana and Michigan to get a sense of what may happen in Wisconsin.

Economists and others who study the issue say it’s too soon to draw conclusions from either state about what effect right-to-work is having. But that hasn’t stopped both sides from turning to Indiana and Michigan during the contentious debate.

Under right-to-work, private-sector businesses cannot enter labor contracts that require workers to pay union dues. Supporters say that it’s about worker freedom and that right-to-work will make Wisconsin more attractive to businesses looking to move in or expand. But opponents say the goal is to destroy unions, which they argue will hurt the economy, lower wages and endanger workplace safety.

Michigan has seen declines in union membership since right-to-work took effect there, and that’s not even accounting for Detroit automakers with contracts due to expire in September.

Michigan had one of the sharpest year-to-year drops in union membership nationwide last year, declining from 16.3 percent in 2013 to 14.5 percent. The decrease came in the first full year under the state’s right-to-work law, after union membership dipped slightly in 2013 when the law was in effect for nine months.

Union officials say another driver for the drop is a 2012 law that received less attention. It declared that 42,000 in-home health care workers were no longer eligible to be represented by a union because many were family members being reimbursed by Medicaid. Unions were unable to overturn the measure at the ballot box.

While union membership is down, Michigan economic development officials have been unable to provide any examples of businesses expanding or locating in the state because of the law. Republican Gov. Rick Snyder, though, has said some companies had refused to even consider Michigan before it became a right-to-work state.

Scott Manley, a lobbyist for Wisconsin Manufacturers and Commerce, makes similar arguments for Wisconsin, saying the state is being passed over by companies that won’t even consider it without right-to-work.

He points to Indiana as a success story.

The Indiana Economic Development Corp. reports that since right-to-work took effect in 2012, companies behind 107 new projects or expansions cited it as a factor in their decision to locate or expand in the state. These projects account for about 10,370 projected new jobs and more than $3.4 billion in investment.

“We’d like to put Wisconsin in a position to compete with those kinds of projects that Indiana is getting right now,” Manley said during an Assembly hearing on the bill this week. “Businesses view right-to-work states as having a more favorable business climate.”

In 2012, when the right-to-work law was signed, Indiana’s union membership was at its lowest point in 25 years with just 9.1 percent of all workers members of unions. Since then, union membership has actually risen to 10.7 percent, a jump some have said is not surprising given that the law was passed while the state was still recovering from the recession and since then economic development has increased.

Michael Hicks, director of the Center for Business and Economic Research at Ball State University, said it’s too soon to link the increase to the right-to-work law or conclusively isolate its impact. Abdur Chowdhury, an economics professor at Marquette University, agreed it’s too soon to know what effect the laws have had in Michigan and Indiana.

He said it would be better to examine Oklahoma, which enacted its law in 2001, the third most-recent state to do so. Union membership there dropped from 8.6 percent the year the law went into effect to 6 percent last year. And most of the economic indicators show that Oklahoma is worse off than Wisconsin, Chowdhury said.

Chowdhury predicted that making Wisconsin a right-to-work state will result in a loss of $4.5 billion in income, along with reducing unions’ power. Union membership in Wisconsin has already been steadily declining, from 17.8 percent in 2000 to just 11.7 percent last year.

“There’s no economic reason to support a right-to-work law,” he said.

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Associated Press writers David Eggert in Lansing, Michigan, and Lauryn Schroeder in Indianapolis contributed to this report.